With the popularity of Internet Protocol (IP) technique, a Next Generation Network (NGN) has been widely applied, which uses an IP network as a bearer network.
A basic architecture of existing NGN is shown in FIG. 1. The NGN includes a soft switch, various terminals and gateways. The soft switch, as a core device in NGN, is used for translation between signal address and IP address, translation between different signals, and management of subscribers. The terminal is used to register signal address and IP address with the soft switch, initiate and receive calls, and code/decode audio and video data. Viewed from the mechanism, the gateways have the same function as the terminal, including registration, call, and audio-video codec function, etc. The gateways differ from the terminals in that they have larger capacity and better performance, and mainly used for intercommunication between NGN and conventional PSTN.
It can be seen from FIG. 1 that the soft switch, which is the core device of NGN, is directly connected with the terminal via IP bearer network, that is to say, the NGN is a network with a “flat” architecture. The flat network architecture is adaptable at the early stage of NGN development since the NGN has a small scale and is used for trial, which has less strict requirements of network performances, such as security, reliability, etc. However, with the commercialization of NGN, the flat network architecture shows some disadvantages as follows:
1. Network Address Translation (NAT) technique is widely used due to lack of IP addresses. However, NGN terminal subscribers under NAT can not access the NGN core network directly.
2. Increasing attacks, especially signaling attacks, in the IP bearer network, bring serious threat to the NGN core network.
3. An obvious difference of the NGN from the conventional PSTN is that signaling is processed separately from media. Signaling streams are processed through the soft switch but media streams are not, which can result in bandwidth stealing.
In view of above, a Session Border Controller (SBC) device is introduced in the NGN, as shown in FIG. 2. The SBC device functions as both signaling proxy and media proxy. For the terminal, the SBC device serves as the soft switch. For the soft switch, the SBC device serves as the terminal. In this way, the NGN core network is separated from the subscriber access network to assure the security of the NGN core network. Upon introduction of the SBC device, the SBC device serves as the proxy of all media streams of all terminals, which can solve the problem of bandwidth stealing.
In order to ensure high availability of NGN, there are usually two soft switches configured in the NGN core network, which serve as a backup of each other. The terminal supports a “dual homing” function. By configuring addresses of primary and standby soft switches, continuity of terminal traffics will not be affected if one of the soft switches fails. However, a new problem arises with the introduction of SBC device. The SBC device is connected between the NGN core network and the subscriber access network, so a large amount of traffics of the terminal subscriber will be interrupted in case of failure of the SBC device. Therefore, it is necessary to configure a backup for the SBC device.
A preferred embodiment is shown in FIG. 3.
Both terminal A and terminal B support the dual homing function. During normal operation, the soft switch works in a load sharing mode. Terminal A registers with the soft switch through device SBC-A and terminal B registers with the soft switch through device SBC-B.
Under ideal condition, if soft switch A fails, terminal A can detect the failure of soft switch A and register with soft switch B through device SBC-B. In addition, soft switch B can detect the failure of soft switch A and take over the traffics of soft switch A, so that the traffic continuity is ensured.
However, if device SBC-A as shown in FIG. 3 fails, terminal A will register with soft switch B through device SBC-B since soft switch A is unreachable, but soft switch B will not take over the traffics of soft switch A and will thus reject the register request because soft switch B does not detect the failure of soft switch A, which results in traffic interruption. This embodiment just shows one case that the introduction of SBC device results in a single-point failure. There will be various single-point failures in the case of concatenation of multiple SBC devices. The above is resulted from that the SBC device can not support dynamic signaling routing.